Dear Lifehacker,
I'm looking to buy a new digital camera, but I don't know what specifications matter. I've been told megapixel ratings don't really matter when it comes to image quality, so what do I look for? What specs will tell me if a camera shoots great images or not?

Sincerely,
Spec'd Out

Dear Spec'd,
You're right. Megapixel ratings—meaning the number of megapixels a camera can capture in a single shot—is pretty much irrelevant when it comes to image quality. If anything, a high megapixel rating on a small camera is often a bad sign. When companies pack too many megapixels into a camera, images can get a little noisy because so much information is being captured in a small space. As technology is becoming better, this is becoming less of a problem. Nonetheless, don't rely on a megapixel rating to discover whether a camera can take high quality photos. Like megapixels, many specifications you'll see advertised on a camera box will not indicate image quality, and, ultimately, you're not going to know if a camera can take beautiful photos by looking at its technical details. But there are specifications that can tell you a few things about a camera's image quality potential, and they all relate to its sensor.

The Sensor

A digital camera sensor is, basically, its film. When you take a photo, the sensor is exposed to light and other components in the camera record what it sees. There are many, many types of camera sensors and it would be wasteful to compare every last one, but there are a few you should know about. Here are the four that really matter right now, organized by size from small to large.

Cellphone and Point-and-Shoot Sensors

Cellphone and point-and-shoot sensors are generally pretty tiny, and they try to pack a lot of information into their small size. This often results in poor image quality because a tiny little sensor can only do so much. Quality is sacrificed in a couple of ways. In general, light is an issue. If there isn't plenty of it, many small sensors will struggle to see. Because they're tiny they can only be exposed to so much light, and this often hinders their performance. Of course, the iPhone 4S' camera is a great example of an exception. Tiny sensors are getting better, and so are the image processors associated with them. When a small sensor struggles in low light situations, the camera's (or phone's) image processing abilities can try to compensate. They can brighten up dark areas and try to pull detail out of overly-lit sections of an image. This is often beneficial, but it comes at a price. If you've ever tried to brighten up a photo that's too dark, you know that it gets noisy/grainy when you do. Image processors know this, too, and therefore try to reduce that noise. That reduction will cause the image to look a little less sharp, and sharpness is already a problem with small sensors in the first place.

While sensor size won't matter much when it comes to cellphone cameras, it can matter with point-and-shoots. The more compact your point-and-shoot, the smaller the sensor is likely to be. When you have a smaller sensor, the manufacturer is going to have to compensate for its deficiencies in some way. While a smaller sensor won't always equal poorer image quality, you have a better chance for better images with a bigger sensor.

Micro-4/3rds Sensors

The Micro-4/3rds system was created as a compromise between big digital SLR (DSLR) cameras and point-and-shoots. The idea was to provide a compact system with interchangeable lenses that provided high image quality. Thanks to the larger sensor size and the fact that you can choose your lenses, these cameras can provide much higher-quality images while still feeling portable enough for many people.

APS-C Sensors

APS-C sensors are most common in digital SLR (DSLR) cameras, but are sometimes found in compact cameras like the Sony NEX series. They are significantly bigger than what you'd find in a point-and-shoot camera or a cellphone, and this is largely their advantage. Whereas smaller sensors struggle with capturing a lot of light, larger sensors don't suffer as much from this problem. You also have greater control over the depth of field in an image, meaning you can more easily render an out-of-focus background behind your subject. APS-C sensors do have one common disadvantage, however, and that's crop factor. Crop factor refers to how lenses are magnified when attached to APS-C-based cameras. This means that if you attached a 28mm lens it would be magnified to look more like a 45mm lens. Basically, things get zoomed in a little bit. This isn't really a big deal but it's important to know. If you need to take a wide image, you need to buy a wider lens. While 28mm lenses would look plenty wide on a 35mm film or full frame camera (which we'll discuss next), they might not be sufficient on a digital camera with an APS-C sensor.

Full Frame Sensors

Full frame sensors are considered to be the digital equivalents of 35mm film. You'll find them on high-end digital SLR cameras like the popular Canon 5D series. The primary benefit of the full frame sensor is that there is no crop factor. As previously mentioned, APS-C sensors have a crop factor that magnifies attached lenses. For example, on an APS-C-based camera a 28mm lens would look more like a 45mm lens on a regular camera. On a full frame camera that lens won't be magnified at all. It'll look like a 28mm lens. As you've probably figured by now, larger sensors have greater potential to capture more light and so they often handle low-light situations better than smaller sensors. They also are capable of producing a very shallow depth of field, just like a 35mm film camera. Being one of the largest sensors, full frame cameras are often produce some of the highest quality images. This isn't a given, but you can set your expectations high.

The bottom line is this: biggest sensors tend to produce higher-quality images. This is not always the case, but you'll rarely see a cellphone image rival one from a DSLR. While you definitely need to pay attention to more than a camera's sensor, it's a good place to start when comparing specifications.

The Image Processor

A camera's image processor can affect quality in a few ways, many of which are irrelevant if you're shooting in RAW and not JPEG. RAW images are just the data the sensor sees, completely unprocessed. This is great if you want to process the images yourself, later. If you're using a point-and-shoot, or just plan to shoot JPEGs, the processor matters. Many cameras can fix lighting issues and adjust various other settings that can make your images look really nice. A good image processor makes it possible for the camera to handle these operations. It also makes it possible for a camera to capture images in quick succession. While this won't affect image quality directly, being able to capture a few images can mean the difference between getting a good shot and a great shot. A fast processor can actually make a big difference in these ways, so don't disregard it even if you don't need to shoot a lot of photos quickly. A camera's speed is important, as a fast processor can allow a camera to compensate for less-than-ideal lighting conditions.

The Optics

Long-time owners of DSLRs, or cameras with interchangeable lenses, know how important a good lens can be. The lens is the eye of your camera. If it can't see well, your images aren't going to be very good. The optics on a point-and-shoot camera are generally going to be of limited quality because they're 1) pretty tiny and 2) fixed to the camera. There are few specifications that will tell you anything about their quality unless you dig into some very technical reviews. There are, however, a few things you can look for. With any lens, you'll want to know its maximum aperture, or how wide the lens can open. A wider aperture means it can let in more light. More light means you can take photos more easily where there isn't a lot of lighting. Apertures are rated in f-stops, so when you're looking at a lens you'll often see something like f/3.5 attached to it. That means it has a maximum aperture, or f-stop, of 3.5. This is a pretty standard number. Wide apertures are generally considered to be in the range of f/1.4 through f/2.8. If you need a camera that can photograph easily in lower light, looking for a wide aperture is a good place to start.

You'll also want to consider the sharpness of the lens. You won't find this in the specifications, however, but rather in tests. Ultimately, when you're trying to determine if a camera is capable of high-quality images there are two things that will matter: 1) reviews with image samples and 2) your own experiences. The best thing you can do is go out and buy a camera you want to test from a store with a good return policy. Plan to try out the camera for awhile and return it if it doesn't live up to your expectations. If you can't try out the camera or want to do research in advance, one of the best sites for samples and comparisons is Digital Photography Review. While comparisons can get a little technical, they offer plenty of good information that everyone can benefit from. They also provide plenty of samples from technical tests and real-world situations. The best judge of how a camera performs in terms of image quality is going to be your eye. If it meets your needs, it's good enough.